This invention relates to curtain walling components and constructions.
A common form of multi-storey building construction employs a main, load-bearing structure, e.g. of reinforced concrete, comprising floor slabs at each storey, with the outer walls of the construction formed only by relatively lightly loaded curtain walls supported from the load-bearing structure, in particular the outer edges of the floor slabs. The curtain walls are typically metal-framed structures of mullions (vertical frame members) and transoms (horizontal frame members) with an infill of panels or glazing of various types, these structures being arranged to be weathertight and to resist wind loads but their weight being supported by the load-bearing structure.
From such causes as the aging of a building and the loads imposed on it, and changes of temperature, various movements take place and the curtain walls must be able to accommodate these while maintaining their integrity. Thus, aging of a reinforced concrete building can result in a shrinkage or creep phenomenon known as "slump" in which there is a small but steady downwards flow of the main cast structure tending to produce a small but measurable shortening: it may be required to allow a shortening of 1 to 1.5 mm between successive floors of the building for this. Then there are live load deflections on the floor slabs, which can vary between different designs and uses but typically it might be necessary to allow for a maximum deflection of about 6 mm at the edge of each floor slab. In addition, there are temperature effects, partly due to the differences between interior and exterior temperatures and also due to changes of temperature in the different materials used in the construction, and for these effects a difference of about 3 mm per floor must be allowed between the curtain walling and the load bearing structure. Through the combination of these different causes it may be necessary to allow for a maximum relative movement of over 10 mm between the curtain wall frame structure and the floor slabs over the span of one storey.
Conventionally, relative vertical movements have been accommodated by having a series of short mullion members each extending between a successive pair of floor slabs and attaching the ends of each said mullion member to the two floor slabs so that there is a gap between its adjoining mullion members above and below it, one of the end attachments also permitting relative vertical movement between the mullion member and the floor slab. This results in the expansion gap being located intermediate the height of the infill members that will extend between the top of the upstand rising from the edge of the floor slab and the level of the ceiling below the floor slab. the gaps between the relatively short mullion members allow relative movement between them. The infill is undersized relative to the nominal vertical spacings of the transoms above and below the gaps so that it does not hinder the contraction of the gap. This results in the bottom edge of the infill panels resting on each transom below it and there being a substantial clearance between the top edge of the infill and the transom above it.
This however is unsatisfactory. In the first place, repeated changes of the gap dimensions as slight vertical movements occur can result in the displacement of the seals around the infill, so that in the course of time the sealing effect is less than satisfactory and rain can penetrate the curtain wall. Also, the maixmum gap that can be allowed at the top of the infill members is limited, because an excessive gap would make sealing more difficult and can even affect the security of retention of the infill, especially as some side-to-side clearance might also be required to accommodate the usually smaller horizontal movements. Since the possible maximum vertical gap is limited, it is essential to introduce the expansion breaks between each successive pair of floor slabs, and even then it may be difficult to provide a satisfactory result if the dimensions and/or loading of the construction requires a large expansion gap--in particular with larger temperature differentials and floor spacings or with greater live load deflections, as might be required in earthquake zones.
It is known from British Pat. No. 1,531,593 to arrange an array of glazed metal frames to form a curtain wall of a building. Each glazed frame has a bar running across it intermediate its height to provide for its connection directly to the load-bearing structure of the building to support the frame, independently of the other frames of the array. Extreme ends of each bar have further connections with the load-bearing structure that accommodate vertical sliding movements, these being intended to hold the respective frame against wind forces. Finally, there are tenon pin connections between vertically successive frames that fix the frames together except for vertical sliding movements.
It will be noted that this construction provides only for vertical displacements. However, this is not sufficient to accommodate transient loads and longer term movements of the building as a whole. In particular, it can be expected that both transient loads and long-term movements of the building structure will occur horizontally in the plane of the curtain wall as well as vertically. One source of such movements may be the differential thermal expansion that occurs in large size structures. The construction of British Pat. No. 1,531,593 has no means of permitting horizontal movement between the frames of a vertical series, and the unrelieved horizontal forces can have the effect of preventing intended vertical displacements, because they will tend to place side loads on the tenon pin connections which will at least give an increased frictional resistance to sliding and can also deform the pins so that they are no longer able to slide in their receiving holes. These pins will receive further loads from wind forces, unless care is taken to support each frame at the middle of its height to prevent the wind force on the area of the frame producing a resultant turning moment about the bar end connections, and the avoidance of this condition is a considerable restraint on the design of the structure.